Pressure Swing Dehydration
DEC.ADM_PSD™
Heatless molecular-sieve dehydration for solvent vapour streams
DEC.ADM_PSD™ (Pressure Swing Dehydration) is an advanced molecular-sieve dehydration technology developed for the continuous removal of water from pressurized solvent vapour streams. The process combines selective adsorption on zeolitic molecular sieves with pressure-swing regeneration, providing an energy-efficient, heatless alternative to thermal regeneration systems for applications where very low residual water content is required.
The technology is particularly suited to solvent mixtures containing alcohols, esters and other organic compounds that are processed in the vapour phase under pressure and subsequently condensed for recovery.
How it works? • DEC.ADM_PSD™
The DEC.ADM_PSD™ skid consists of three molecular-sieve adsorbers — MS-A, MS-B and MS-C — operated in a cyclic n-1 configuration: two beds adsorb while one regenerates, so dehydration runs continuously. As an adsorption bed approaches its moisture-loading limit, it is switched out and regenerated by controlled pressure reduction, then returned to service. Because each bed alternates between adsorption and regeneration, the skid delivers uninterrupted dehydration from a fixed, compact set of vessels.
- Configuration
- 3 molecular-sieve adsorbers (MS-A / MS-B / MS-C), cyclic n-1 operation
- Adsorbent
- DEC.MZA™ zeolitic molecular sieve
- Regeneration
- Heatless Pressure Swing Adsorption (PSA) — no regeneration heater
- Water spec
- Less than 0.1 wt% water in the dehydrated solvent outlet (reference examples)
- Dehydration point
- Before condensation, while the solvent is still pressurized vapour
The incoming solvent vapour contains a relatively small quantity of water. As the pressurized stream passes through the molecular sieve, the DEC.MZA™ zeolite selectively adsorbs moisture, so the solvent-rich vapour leaving the adsorption beds is substantially dehydrated and is routed through a common product line.
Pressurized adsorption, controlled expansion and condensation
The dehydrated vapour exits the active molecular-sieve beds while still pressurized, and the combined outlet stream is routed through a dedicated depressurizing/expansion valve, reducing the pressure before the condenser. The expanded vapour is then condensed using available cooling water (CWS) and collected as liquid solvent downstream. This sequence matters most where the feed arrives as a hot, pressurized vapour and the recovered solvent must ultimately be obtained as a liquid.
Heatless PSA regeneration
Unlike temperature-swing molecular-sieve systems, DEC.ADM_PSD™ needs no dedicated regeneration heater. Regeneration is achieved through Pressure Swing Adsorption (PSA): the saturated bed is depressurized through a dedicated blow-down / desorption valve, and the pressure reduction causes adsorbed moisture to desorb from the zeolite. The resulting regeneration stream — predominantly vapour, carrying released water, residual solvent vapour and other desorbed volatiles — is not vented to atmosphere. Instead, DEC.ADM_PSD™ integrates it with the adsorption section of the DEC.SRU™ Solvent Recovery Unit, recovering the residual solvent within the site's air-pollution-control system.
Individual molecular-sieve drainage
Although the main regeneration mechanism is vapour-phase pressure swing, condensation can occur inside the vessels under certain conditions. Each molecular-sieve adsorber therefore has its own bottom drainage connection, a dedicated pneumatic liquid-drain valve and a separate liquid-drain header. Collected liquid is transferred to a drain/sump collection tank and routed to the DEC.ADM_WPA™ Water Phase Atomizer, where the aqueous/liquid phase is introduced into the appropriate downstream SRU process — preventing liquid from accumulating uncontrolled inside the vessels.
Three-Bed n-1 Architecture: A Representative Cycle
The three-bed configuration gives DEC.ADM_PSD™ its operational flexibility: while two beds adsorb, the third regenerates, and the roles rotate continuously so the molecular-sieve inventory is refreshed without ever interrupting dehydration.
The sequence then repeats, cycling continuously between the three beds.
Pneumatically actuated process valves
The PSD skid uses dedicated pneumatically actuated valves for its principal switching functions, providing independent control of molecular-sieve feed isolation, molecular-sieve outlet isolation, blow-down/depressurization, liquid drainage and downstream pressure reduction. Separating the product expansion/depressurization valve from the individual molecular-sieve blow-down valves is fundamental to the architecture: the product expansion valve controls pressure reduction of the dehydrated solvent stream ahead of condensation, while the blow-down valves are dedicated exclusively to molecular-sieve regeneration.
Integration with DEC.SRU™ and DEC.ADM_WPA™
DEC.ADM_PSD™ is engineered as part of an integrated solvent-management architecture rather than an isolated dehydration package. The molecular-sieve regeneration (blow-down) stream is directed to the adsorption section of DEC.SRU™, where residual solvent vapours are captured and recovered. Any liquid collected from the molecular-sieve bottoms is routed to a dedicated collection sump and transferred to DEC.ADM_WPA™, the Water Phase Atomizer system associated with the downstream SRU process — giving both major PSD waste streams a controlled destination instead of an atmospheric vent.
Why Pressure Swing Dehydration?
DEC.ADM_PSD™ combines molecular-sieve dehydration with heatless PSA regeneration for a compact, energy-efficient solvent-drying solution.
Typical Applications
DEC.ADM_PSD™ is intended for applications where water must be removed from solvent-containing vapour streams downstream pressurized streams, (e.g. pressure distillation columns, DST-p™).
DEC.ADM_PSD™ — Dehydrate First. Condense Later.
By moving the dehydration step upstream of solvent condensation, DEC.ADM_PSD™ separates water from the solvent vapour while the solvent remains a pressurized gas, then expands and condenses the dried solvent downstream:
| Solvent path | Regeneration path | Liquid-drain path |
|---|---|---|
| Pressurized solvent vapour | Saturated molecular sieve | Molecular-sieve bottom drain |
| DEC.MZA™ molecular-sieve adsorption | Heatless PSA decompression | Sump / liquid collection |
| Water selectively adsorbed | Blow-down vapour | DEC.ADM_WPA™ |
| Dehydrated solvent vapour | DEC.SRU™ solvent recovery | DEC.SRU™ |
| Controlled expansion / depressurization | — | — |
| Cooling-water condensation | — | — |
| Dry solvent recovery | — | — |
This architecture makes DEC.ADM_PSD™ a fully integrated dehydration and solvent-management solution, combining molecular-sieve technology, heatless PSA regeneration, controlled solvent condensation and downstream emission-control integration.
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FAQs • Frequently Asked Questions
Pressure Swing Dehydration • DEC.ADM_PSD™
What is DEC.ADM_PSD™?
DEC.ADM_PSD™ (Pressure Swing Dehydration) is DEC's heatless molecular-sieve dehydration technology for pressurized solvent vapour streams. Three DEC.MZA™ zeolite adsorbers operate in a cyclic n-1 configuration, selectively removing moisture before the dehydrated solvent is expanded and condensed downstream.
How does the three-bed n-1 cycle keep dehydration continuous?
At any time two of the three molecular-sieve beds (MS-A, MS-B, MS-C) are adsorbing while the third regenerates. The beds rotate through this sequence, so dehydration never stops even while individual beds are being regenerated.
Why does DEC.ADM_PSD™ dehydrate the solvent before condensing it?
Dehydrating the solvent while it is still a pressurized vapour, before condensation, lets the process treat a hot, pressurized feed and deliver a dry liquid solvent. The dehydrated vapour is expanded through a dedicated valve and then condensed using cooling water, rather than removing water from an already-condensed liquid.
How is the molecular sieve regenerated, and where does the blow-down go?
Regeneration uses heatless Pressure Swing Adsorption (PSA): the saturated bed is depressurized through a blow-down valve so adsorbed moisture desorbs from the zeolite. Rather than venting to atmosphere, DEC.ADM_PSD™ routes this vapour stream to the adsorption section of DEC.SRU™ so residual solvent is recovered.
What water content and solvents can DEC.ADM_PSD™ handle?
Reference applications target less than 0.1 wt% water in the dehydrated solvent outlet, for feed rates of roughly 680–900 Nm³/h at 4–8 barg. Typical solvents include ethanol, isopropanol, ethyl acetate and other compatible organic solvents in mixed vapour streams; final sizing and molecular-sieve selection are application-specific.
Is pricing available for a DEC.ADM_PSD™ system?
DEC.ADM_PSD™ skids are custom-engineered around each customer's solvent composition, throughput, pressure and required water specification, so there is no fixed list price. DEC's Technical Sales & Applications engineering team sizes and quotes each system after reviewing your process data — request a quote via the contact page.
